PROJECT SUMMARY/ABSTRACT Pediatric obesity affects 1 in 3 children in the US and represents a public health crisis [1]. In utero exposure to maternal obesity and caesarean section (C-section) are independently and jointly associated with offspring obesity [2, 3]. Accumulating data suggests maternal obesity and C-section may seed an ?obesogenic? microbiome responsible for transmitting obesity risk from mother to child [4, 5]. Exclusive breastfeeding is associated with protection against pediatric obesity [6]; however, the association between human milk components and the microbiome that account for these observations are poorly characterized. Recent advances in untargeted metabolomics provides a novel opportunity to comprehensively investigate how the human milk metabolome in combination with microbe-host interactions are associated with infant adiposity during the first year of life. The Principal Investigator, Dr. Dominick J. Lemas, Ph.D. will use high-resolution mass spectrometry as a tool to interrogate the human milk metabolome and infant microbiome in a longitudinal maternal-infant cohort of obese and normal weight mothers that includes vaginally and cesarean section deliveries. The over-arching hypothesis of this proposal is that the human milk metabolome will be associated with novel changes in the early infant microbiome that alter risk for obesity and weight gain in the first year of life. In collaboration with a multidisciplinary team of expert mentors (including primary mentor Dr. Christian Jobin and co-mentors Drs. Josef Neu, Timothy Garrett, William Hogan, Janice Krieger), the primary goal of this K01 career development proposal is for Dr. Lemas to develop expertise in high-resolution metabolomics, biomedical informatics and longitudinal clinical microbiome studies. The University of Florida (UF) boasts an intellectually rich research environment that will facilitate these goals. More specifically, longitudinal data collection will be completed at the NIH-funded UF Clinical and Translational Science Institute and human milk and stool metabolomics analysis will be completed at the NIH-funded UF Southeast Center for Integrated Metabolomics (SECIM). Finally, microbial sequencing will be completed at the UF NextGeneration DNA Sequencing Core and high-throughput data analysis will be completed at the UF Research Computing Center. Specific Aim 1 will generate a data-driven recruitment plan using informant interviews and qualitative methods to identify barriers and facilitators to successful participant recruitment and strategies. Specific Aim 2 will characterize the role of the human milk metabolome on the development of the infant microbiome. Specific Aim 3 will identify how the human milk metabolome is associated with infant adiposity. The proposed research is focused on the pathophysiology of infant growth and adiposity during early life and will inform subsequent studies that seek to reduce the risk of pediatric obesity. The structured mentoring and training plan is designed to facilitate Dr. Lemas's long-term goal of developing an independently-funded clinical and translational research program focused characterizing the microbe-host interactions that mediate the protective role of breastfeeding on pediatric obesity, consistent with the mission of the NIDDK.